1. Field of the Invention
The present invention relates to a diesel engine, and more particularly to a diesel engine having an auxiliary combustion chamber such as a swirl combustion chamber or a precombustion chamber, wherein the combustion under a low load such as upon idling is slowed to lower the rate of a pressure buildup within the cylinder for thereby reducing noise and vibrations to a large extent.
2. Description of the Prior Art
FIG. 1 of the accompanying drawings illustrates a conventional diesel engine having a swirl combustion chamber 2 defined in a cylinder head 1 mounted on a cylinder block (not shown). The swirl combustion chamber 2 communicates with a main combustion chamber 3 defined in the cylinder block. When a piston is moved upwardly in the main combustion chamber 3, compressed intake air flows into the swirl combustion chamber 3 to generate a swirl S therein. The swirl combustion chamber 3 has a fuel injection nozzle means 4 for injecting fuel F into the swirl combustion chamber 3. The fuel injected by the fuel injection nozzle means 4 is mixed with air or atomized at a rate increased by the swirl S, and the atomized fuel is ignited by the heat produced by the compressed air and combusted.
If an ignition delay is increased in the diesel engine, then a diesel knock is produced wherein fuel injected during the ignition delay is formed into a pre-mixture creating a high energy condition entirely in the swirl combustion chamber 2, which allows a number of flame cores to be produced and at the same time causes an explosive combustion to go on. The quick combustion increases the rate of a pressure buildup within the cylinder thereby to produce a large pressure wave which impinges upon the piston and cylinder wall, thus generating noise and vibrations. While the engine is idling at a low cooling water temperature, immediately after the engine has started, the temperature of the overall engine is low, and the fuel has poor ignitability, so that the engine is more likely to suffer from knocking. Such engine knocking is also undesireable because it is felt by the driver.
To prevent diesel engine knocking, the ignition delay can be shortened by promoting atomization of the injected fuel as assisted by the swirl S. The reduced ignition delay can increase the fuel ignitability in the overall swirl combustion chamber 2 and reduce noise considerably. However, only an attempt to improve the fuel ignitability fails to suppress the quick fuel combustion sufficiently and also noise generation since a large amount of fuel is atomized to produce an air-fuel mixture even within the shortened ignition delay.